1. Field of the Invention
The present invention relates to a semiconductor laser driving device and a pulse amplifier suitable for use as a pulse current supply circuit in the semiconductor laser driving device. This pulse amplifier varies a pulse amplitude of an output pulse in response to a control signal.
2. Description of the Related Art
Semiconductor laser driving device are used for controlling an excitation of the semiconductor laser, such as a laser diode, used as a light source in an optical communication system. The optical communication system is suitable for a large capacity data transmission, in which a laser diode must be driven at an ultra high transmission rate (G bit/s order). Accordingly, the semiconductor laser driving device and the pulse amplifier used therein, which can operate at the ultra high transmission rate, are required.
The semiconductor laser driving device in the prior art consists of a bias current supply circuit for supplying a bias current to the laser diode, a pulse current supply circuit for supplying a pulse current to the laser diode for exciting the laser diode to emit a light, and an automatic power control loop for controlling the magnitude of the base current and the pulse amplitude of the pulse current to maintain the output light of the laser diode at a constant power. The bias current and pulse current supply circuits are formed by using, as active elements, bipolar transistors having almost the same characteristics.
When the bipolar transistors are used, however, the transmission rate of the semiconductor laser driving device has an upper limit on the order of about 100s M bit/s and, therefore, the bipolar transistor can not be used for a semiconductor laser driving device operated at 1 G bit/s, which will become more necessary in the future. This limitation to the transmission rate is due to a physical characteristic of the bipolar transistor, and therefore, the transmission rate cannot be increased merely by changing a circuit construction of the driving device.
Accordingly, the use of an FET (Field Effect Transistor) capable of operating at high transmission rate, such as GaAs FET, has been proposed for the high speed operating type semiconductor laser driving device.